Determining number of n,gamma reactions

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Determining number of n,gamma reactions

Postby jblokker » Thu Jun 08, 2017 6:50 pm

Hello everyone,

I'm using Serpent for my bachelor thesis and part of this is determining the amount of n,gamma reactions in a certain material. To do this I have used a detector with the response number 102. According to the old manual the output of a detector should contain 13 values, the 13th being the amount of reactions (if I understood correctly), but the version of Serpent I'm using (Version 2.1.25) only gives 12 values. I understand what the first 10 values are, but I can't find anywhere what the last 2 values are, that is to say, I know they are the mean value and relative statistical error, but I don't know mean value and relative error of what. Can anybody help me with this? I have included the detector output and my input below, but without all the energy bins for the source, as there are over 300. Thanks in advance.

DETtarget = [ 1 1 1 1 1 1 1 1 1 1 2.88526E+01 0.00038 ];

Input:

% --- spheres with different radii centered at x=0 y=0 z=0:

surf 1 sph 0.000 0.000 0.000 2.300 % molybdeen

surf 2 sph 0.000 0.000 0.000 27.300 % Moderator

surf 3 sph 0.000 0.000 0.000 37.300 % target

surf 4 sph 0.000 0.000 0.000 57.300 % reflector

surf 5 sph 0.000 0.000 0.000 80.000 %

% --- materials in the spheres:

mat molybdenum -5.14 rgb 255 0 0 % molybdenum with 50% density with red color in plot
42099.09c -1

mat graphite -2.267 rgb 0 255 0 % graphite moderator or reflector
6012.03c -1

mat holmium -8.79 rgb 0 128 127 % holmium target
67165.03c -1

% --- cells located in the spheres

cell 1 0 molybdenum -1

cell 2 0 graphite 1 -2

cell 3 0 holmium 2 -3

cell 4 0 graphite 3 -4

cell 5 0 void 4 -5

cell 6 0 outside 5

set acelib "/home/jblokker/SERPENT_calculations/sss_jeff311u.xsdata"

% --- detectors

det target dc 3 dm holmium dr 102 holmium % --- n,gamma reactions in holmium target

det flux ds 5 1

% --- Geometry plotter

plot 1 1000 1000

% --- Neutron source

set nps 1000000 [200]

src NeutronSource sp 0 0 0 sb 301
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Re: Determining number of n,gamma reactions

Postby Jaakko Leppänen » Fri Jun 09, 2017 9:24 am

The last two values are the mean and the relative statistical error. The detector entries in detector "target" are:

- dc 3 : integrate flux over cell 3
- dm holmium : integrate flux over material holmium (redundant because the spatial domain was already set by the dc entry)
- dr 102 holmium : multiply flux estimators by the microscopic cross section of holmium (Ho-165)

So the result that you get is the integral microscopic capture rate of Ho-165.
- Jaakko
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Re: Determining number of n,gamma reactions

Postby jblokker » Thu Jul 06, 2017 1:48 pm

Thank you for answering my question, but I have another question. I'm trying to determine the neutron flux through a certain surface and I'm using the surface current detector. I expected the output to be the total amount of neutrons that crossed the surface, but the value I got is way to small for that. Could you please tell me what the output of this detector is?
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Re: Determining number of n,gamma reactions

Postby Jaakko Leppänen » Fri Jul 07, 2017 10:43 am

How did you set the DIR parameter in the surface current detector card? The total current (DIR = 0), for example, is very close to zero if the flux is nearly isotropic.
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Re: Determining number of n,gamma reactions

Postby jblokker » Sat Jul 08, 2017 4:36 pm

I set the DIR parameter to outward, like this:

det flux ds 1 1

Surface 1 is a sphere with an external neutron source in the center.
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Re: Determining number of n,gamma reactions

Postby Jaakko Leppänen » Mon Jul 10, 2017 9:54 am

Have you set the normalization?
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Re: Determining number of n,gamma reactions

Postby jblokker » Mon Jul 10, 2017 12:17 pm

No, I have not.
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Re: Determining number of n,gamma reactions

Postby Jaakko Leppänen » Tue Jul 11, 2017 10:56 am

OK, then your results are normalized to unit source rate. See Sec. 5.8 in Serpent manual for different normalization options.
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Re: Determining number of n,gamma reactions

Postby jblokker » Wed Aug 02, 2017 1:36 pm

Okay, thank you, I'll see if I can solve it using a different normalization.
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